Every Śiva temple has the figure of a white ,black humped bull reclining on a raised platform and facing the entrance door of the shrine so that, Nandi is considered to be one of Śiva’s chief attendants and occasionally is depicted in sculpture as a bull-faced dwarf figure. Nandi is known also in a wholly anthropomorphic form, called variously Nandikēśvara, or Adhikāranandin.
Nandi occupies an axial position, focusing the attention of the faithful from the outer halls of the temple directly into its spiritual heart, the 'garbhagrha', or 'womb-chamber'. Images of this scale and larger were usually housed in a pillared hall or 'mandapa', which stood independent of the principal shrine and was orientated toward the east, facing directly into the temple, so that Nandi's intimate relationship with Shiva .
Nandi is the bull vahana of Shiva. In many Shiva temples, Nandi is placed directly opposite the entrance to the shrine containing the central image of Shiva, the shiva linga. In this position, Nandi is acting not only as Shiva's guardian, but also as a constant devotee. As Nandi mimics the position of every devotee who comes to stand before the deity, he is often revered as a model devotee.
His guardian is Nandi (the white bull), whose statue can often be seen watching over the main shrine. The bull is said to embody sexual energy, fertility. Riding on its back, Shiva is in control of these impulses.
In the Panchanadha Shetram, Nandhi is described as a very staunch Shiva devotee who will never tolerate any unbecoming word about Lord Shia. Once during Daksha Yagna , Daksha spoke rudely of Lord Shiva and Nandi closed his two ears, chanting "Siva , Siva".
As an independent deity, the bull was known in ancient India as Nandikeshvara, the Lord of Joy, often represented as a man with a bull's head. Nandikeshvara was a rishi who offered service to Shiva by guarding his door.
Lord Shiva has various names describing his association with Nandi. Vrishavahanamurti, the form of Shiva resting against Nandi, is the form he assumes when blessing devotees with freedom from the cycle of existence.
Mahanandishwara is the presiding deity of Lord Shiva that resides in Mahanandishwara temple in Mahanandi. Within a 15 kilometer radius from the temple lie nine Nandis known as "Navanandis". Mahanandi temple is one of the Nava Nandis, and the other eight temples Prathama Nandi, Naga Nandi, Vinayaka Nandi, Garuda Nandi, Shiva Nandi, Vishnu Nandi, Surya Nandi, and Soma Nandi.
Nandi Pooja On this day, Sri Nandeesvara must be worshipped as part of Rishaba pooja. One of the important facets of this worship is cleaning up the Nandi sanctum in the temple. Make sure you do not use any sharp implements or your finger nails in the cleaning process. Do it with utmost care. Apply coats of sesame oil and coconut oil to Sri Nandi's divine frame. Apply turmeric paste and sandalwood paste and circunambulate Him 108 times. This is the first part of Nandi worship on the day after Pongal.
On this day, recite all your improper thoughts, evil dreams and the like in the ear of Lord Nandi. Whatever secrets you may be bottling up within yourself, tell them to Sri Nandi. You may be wondering that if you mention it any human, it may have adverse effects. You may feel that you can't tell it any soul. That's ok, but don't bottle them up inside you; just reveal all these innermost secrets, irrespective of whether they are good or bad, to Lord Nandi on the day after Pongal and request expiation from Him for these improper thoughts, desires and secrets. Sri Nandeesvara will do the needful and take care of you.
In the days of yore, people sought expiation for a day's bad karma on that day itself. Thus they did not accumulate any bad karma at all. Because of their conscientous efforts to lead a karma free life, they were promoted to the post of pithru devas.
Lord Nandi is the patron saint of all bulls everywhere. On this day after Pongal, make sure you do Go Pooja, Rishaba Pooja and also Kaarunya Tharpanam rites for all living things, including animals, birds and insects.
The big bull on which Lord Shiva rides.It is believed that before entering the temple of Shiva we are to take his permission.
Nandikesa Maha Bhaga, Shiva dhyana parayana,
Gowri sankara sevartham Anugnam dathumarhasi.
(Oh Lord Nandi who is Lord of all bulls,
Who is immersed in prayer of Shiva,
Please give me permission,
To worship Lord Sankara with his consort Gowri.)